The prior art has recognized that if the arc burns angularly instead of vertically in alignment with the arcing electrode, the arc flare is directed more intensely against the side wall, in the direction of the arc angularity, so as to result in premature destruction of the area of the side wall that is affected. This has led to a number of proposals for insuring that the arc burns vertically in alignment with the arcing electrode.
One example of such a proposal is exemplified by the Lassander and Stenkvist U.S. Pat. No. 4,403,328. Another proposal is embodied by the Bergman and Stenkvist patent application Ser. No. 622,589, this proposal being described hereinafter in connection with disclosing the present invention. Such proposals have been generally effective in providing for the arc burning vertically.
Normally the arcing electrode is positioned concentrically with the furnace side wall and hearth both of which are as symmetrically circular as furnace construction techniques permit. Therefore, with the arc burning vertically on the axis of the furnace it has been assumed that the arc flare should be uniformly distributed circumferentially against the side wall so as to provide uniform side wall life, avoiding a premature furnace shut-down as is required even if the side wall is only locally destroyed at one place. Unfortunately this assumption has not proven to be entirely correct, localized side wall destruction being experienced although the arc burns vertically.
The object of the present invention is to provide some means for effecting what might be called a fine tuning of such a furnace to prevent subsequent localized side wall destruction after it initially occurs in the furnace working under commercial production conditions.